Production of high grade sheet and strip steel from nonrefined molten steel



Feb. 20, 1940. T. sENDzlMlR 2,191,355

PRODUCTION OF HIGH GRADE SHEET AND STRIP STEEL FROM NONREFINED MOLTEN STEEL' l Filed NOV. 30, 1937 2 Sheets-Sheet 1 hal. E612.

, 4av Q 1NVENTOR. TAaEz/.sz SE/vazv/M/R.

ATTORNEY.

Feb. 20, 1940. T, SENDZ|M|R 2,191,355'

PRODUCTION 0F HIGH GRADE SHEET AND STRIP STEEL FROM. NONREFINED MOLTEN STEEL Filed NOV. 50, 1937 n 2 Sheets-Sheet 2 had.

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IN VENTOR. TAaEz/.sz flvaz/M/e.

ATTORNEYS.

Patented FebQZO, 194@ PATENT OFFICE raonUcTlon oF man GRADE SHEET AND STRIP STEEL mom NoNaEFiNEn MoLTEN STEEL Tadensz Sendzimir, Paris, France Application November 30, 1937, Serial No. 117,296 YIn Germany December 3, 1936 is claims.' (ci. zii-14s) This invention relates to the production of high grade sheet and strip steel from a relatively low grade steel at a considerably reduced production cost. In conventional practice in the productionvof high grade sheet steel. such as automobile and` deep drawing steel an especially refined material is used at the start. During the course of production further treatment is carried on in the pouring ladle and the material is subsequently carefully poured into the ingots and thereafter is hot and cold rolled to the desired finished gauge. The sheets are then annealed or normalized and subsequently pickled.

In accordance with my novel process the starting material is one of lower refining properties,

in-which decarbonization, deoxidation, and the removal of sulphur have not necessarily been carried as far as is usual in conventional processes. My method is based on a gradual surface refining process which is carried out during subsequent processing steps, so that the surface becomesprogressively more refined, ductile and softer. Furthermore, as the strip gauge is reduced the thickness of this refined surface increases.

I prefer to pour themolten steel into rotating cylindrlcally shaped molds according to con;- -vention'al centrifugal casting methods. 'Ihe ingots thus produced are hollow and the axial length of these ingots approximates the width of the finished product. The thickness of the cylindrical wall of such an ingot may be from 20 to 100 millimeters. If proper pouring and cooling methods are used in connection with an ingot of the above mentioned thickness, `segregation and liquation are substantially eliminated.

The hollow ingots after surface solidiflcation are placed into pit furnaces of special construction where they undergo a refining process. Preferably, electric heating devices are used in order to secure a clean, dust and slag free furnace atmosphere. The proper design of the furnace and proper selection of a heat insulating material reduce the external heat requirements to a negligible value. Within this furnace a reducing and decarbonizing atmosphereis maintained. y.

The refining. process which may last several hours is predicated upon surface absorption of hydrogen and other gases which deoxidize and decarbonize the steel to a depth of several'millimeters. Sulphur removal also takes place to a large degree, and it maybe assumed that other reactions also take place which result in improved properties of the finished sheets. The process is gradual and is similar to the process of carbonization by cementatlon. As the process continues, the refined surface skin gradually increases in thickness or in other words, the refining action penetrates more deeply into the material. Forsteels which need noy further decarbonization the partial pressure of carbon bearing gases in the pit furnace atmosphere is increased up to the necessary balanced condition. Degassing of the ingot may be carried out by means of a partial vacuum ln the pit furnace throughout 'the entire heat treatment or during a partialphase thereof. For this purpose there may be provided a liquid seal of molten lead at the top of the pit furnace. Thus a reduction of the surface scale and a deoxidation and decarbonization of the ingot to a depth of several millimeters may be accomplished by absorption of the gases present in the pit furnace, and thereafter by 'means of the above noted partial evacuation of the furnace atmosphere, a largepart of the gases present in the ingot as well as newly absorbed gases may be removed.

The hollow ingots are then removed from the pit furnace in a condition in which they have been homogeneously heated tothe proper rolling 25 temperature. I have found it advantageous to select a rolling temperature which is lower than conventional rolling temperatures for the hereinafter described rolling process, thereby pre- `venting the formation of thick or peeling scale during the short time the ingot is exposed to the atmosphere. I have founda rolling temperature from 900 C. to 1050 C. to be satisfactory. These hollow ingots may be rolled into an endless band on a special mill or they may be cut and rolled on a conventional strip mill. Preferably, the rolling processes are carried out in the absence of air or under the protection of reducing gases. The hot strips after this rolling are subsequently further'rened in either coiled or at 40 condition.' 'I'he tougher surface skin which has been provided up to this point protects the surface against possible defects during the hot rolling process, and the possibility of checking is positively prevented whereby side trimming of the strip is obviated. Furthermore, the surface of the strip is completely scale and slag free, whereby descaling processes prior and during hot rolling, as for example the squeezing of the strip or the application of high pressure water sprays, as has been found necessary in conventional methods, are thus eliminated.

In subsequent refining of a coll strip the cooling of the coil takes place in special containers which win be described hereinafter. special -precaution is taken to maintain a special atmosphere in these containers. During this latter process a spontaneous annealing of the material takes place, i. e., grains which elongated during the rolling processes grow and lose their directional properties. Dissolved hydrogen and other gases in the particular furnace penetrate deeper into the metal on account of the prolonged diffusion of these gases.

At this point in the process the thickness of the hollow .ingot may be from 1.5 to 3 millimeters and above, and lpenetration is almost complete. omitted in the pit furnace it can be added as a degassing process in the strip coil annealing y chamber. This latter phase of the process may also be added to produce scale free surfaces. 'Ihe second vacuum treatment may be added independently of the first vacuum treatment in the pit furnace. 'I'he first treatment may not produce penetration to the middle sections of the wall of the hollow ingot due to its comparative thickness at that point in the process.

An alternate process may be carried out for certain grades of steel. The reducing atmosphere in the pit furnace may be provided with a carbonizing effect whereby there is produced an olrygen-free but higher carbon content surface s n.

The surface of the material is thoroughly decarbonized under reducing conditions in the above described cooling and annealing furnaces after the hot rolling process. At this point of the process the penetration is much deeper on account of the! preceding hot rolling of the strip. Decarbonization of the coiled strip during the annealing and cooling processes is considerably slower on account of impaired entrance of the gas into the strip surface. However, by virtue of the fact that rapid diffusion of thecarbon content in the thin and carbonized skin toward the inner part of the strip is taking place, there is produced a strip of an average carbon content which is often desirable.

A further alternate process for annealing and cooling may involve the pulling ofthe coiled strip through a strip furnace under special atmospheres and a subsequent vacuum treatment. The only difference between the second and the first process would be in the better access of the gases into the strip surfaces which would result in deeper diffusion of the gases into the metal.

Both processes`produce a cooled strip with an absolutely clean surface whereby pickling prior to cold rolling is rendered unnecessary. Improved cold rolling is attained by the further development of the tough metal skin in the annealing furnace. Checking of the strip is prevented as above pointed outnand the strip surface has far better properties than ythe surfaces produced by conventional methods.

I'he cold reduced strip is subsequently annealed or normalized. At this point of the process the invention is applied to completely deoxidize and decarbonize the strip. For this purpose strip is pulled through a furnace in which itis heated to the required annealing or normalizing temperature under the influence of a suitable furnace atmosphere. and is kept at this temperature until the effect of the above described rening process has partially or completely penetrated the strip. A subsequent vacuum process may be added.

If the vacuum treatment has beenr of a pit furnace for processing the hollow ingots prior to hot rolling.

Fig. 2 is a view similar to Fig. l showing the manner in whichthe ingots may be charged into and removed from the furnace.

Fig. 3 is a diagrammatic plan view showing a desirable arrangement of pit furnaces.

Fig. 4 is a cross sectional view of a furnace used in connection with the hot rolling of the ingot taken on the line 4-4 of Fig. 5.

Fig. 5 is a longitudinal cross sectional view taken on the line 5 5 of Fig. 4 and showing a two high hot mill in connection with the furnace.

Fig. 6 is a central vertical cross section showing another arrangement of a furnace and mill in which the ingot is ,shown in an early phase of the rolling process.

Fig. 'I is a view similar to Fig. 6 showing the rolling during a later phase of the process.

Fig.y 8 is a vertical longitudinal section of a cooling chamber for the hot rolled and coiled strip.

Fig. 9 is a detailed cross sectional view similar to Fig. 8 showing the sealing arrangement for the chamber bell.

Fig. 10 is a view similar to Fig. 8 of a modification of the cooling chamber.

The pit furnace shown in Figs. 1, 2 and 3 comprises an insulating base 9, a base plate 8 and walls 2|. A desirable honeycomb arrangement of the individual pits is shown in Fig. 3. The hollow ingot I rests on a member 2, which may be aring or a number of blocks annularly disposed. A cylinder 3, is located internally of the ingot to provide support for the lid I1 and the heating elements 4. A cylindrical shell I5 provides additional support for the furnace walls 2| and also serves in connection with a liquid seal indicated generally at I3. The lid I1 is provided with an outer cover or bell I4 which dips into the liquid seal. The atmospheric pressure within the furnace chamber may be lowered by the selection of a relatively high outer bell member I4 whereby a higher sealing liquid level may be obtained on the inner side of the member I4, as indicated at I6. Where it is not necessary to maintain a pressure difference within the furnace other types of seals such as dust seals may be used.

The wires 6 provide leads for the heating ele-l then lowered into the pit and the hooks I9 thereof are turned and engaged under the ingot which is then removed from the furnace and quicklyfed into the hot mill. Ihe use of the member 20 will be clear from a consideration of Fig. 2. Since the hooks I9 lill most of the available space 4between the cylindrical shell- I5 and the ingot I,

a proper balancing of the ingot during charging and removal thereof into and from the furnace is insured.

In Figs. 4 and 5, I have shown an ,element for hot rolling the pre-processed hollow ingot. A mill 30 is provided with working rolls 3|, 32, and a drive which is not shown inasmuch as it forms no part of my invention. Mechanism is also -providedinot shown) for feeding the hollow ingot into the mill. This may be accomplished by removing one of theworking rolls or a roll bearing. The looping roll 34' may be removed by anv axial motion. Directly beneath the working rolls I have provided a roller table 35, so that as the cylindrical ingot is reduced, it will gradually touch l the roller table 35. If the loop being rolled is touching the roller table 35, it will be clear that if the rotation of the mill rolls is as shown in Fig. 5, an increase in the speed of the roller table 35 will cause a l`oop to form toward the left side of the mill, so that when the loop has grown suiiiciently the roller 34 may be inserted into the loop. Thereupon the speedof the roller table is reduced below the peripheral speed of the working rolls, whereby the loop in its fur-A ther growth will form toward the right hand side of the mill, whereby the roller 4I may ultimately be introduced into the loop.

I have indicated generally at 36 a furnace for I`holding the heat of the strip during the rolling process. This furnace may be provided with aI reducing atmosphere so that a reducing process may take place at the same time as the rolling process, and by means of a lowered furnace temperature, surface oxidation of the strip is`prevented. Insulating walls are shown at 44 and 45, and the furnace is provided with rails 43 for .the carriages 42 upon which is mounted a freely turning roller 4I. A mechanism for moving the carriages 42 in the furnace is provided by means of the chain 40 and the sprockets 39 and 48 driven by the motor 49.

For heating the furnace I prefer to provide sectional heating elements 46. Suitable gas is fed into the furnace through the pipe 41. The front wall of the furnace is made quickly removable for the purpose of introducing the strip into the furnace. In charging the furnace when the loop of the strip has grown to a sufficient size, the front wall I5 is removed and the roller 4I is run out of tlm furnace by means of its carriages 42. The roller 41 is then removed fro-m the carriages 42, inserted into the rapidly forming loop in the endless strip and replaced on the carriages. The assembly is then pulled back into the furnace by means of the chains 40. The roller 4I is puled back into the furnace until the strip loop is raised from )the roller table 35. The front wall 50 is then replaced. It will be noted that this front wall is provided with seals 31 and 38 for the upper and lower flight of the strip. It will, of course, be understood that if necessary or desirable, the strip may be put under tension. The operations outlined immediately above must be done very' rapidly in order to eliminate gas loss and interruption of the rolling process. When the rolling process is complete, the strip 33 is cut and subsequently coiled. l

In Figs. 6 and 7 I have shown an alternate arrangement inA a rolling mill and furnace for rolling hollow ingots. In these figures I have shown protecting gas.

ing elements because a reducing atmosphere free' from ashes, slag and other deleterious constituents -is desired, so that the surface properties of the strip will not be impaired. A suitable atmosphere may be provided within the furnace by leading into it an appropriate gas by means of the pipe 19. It maybe satisfactory to use internal combustion .motors such as Diesel motors for the mill drives, and in such cases the exhaust` gasesof these motors may be fed directly through the pipe 1li alone or mixed with other gases. Such mill drives can produce suicientamounts of exhaust gas for this process, not only for the furnace requirements duringl hot rolling, but for furnaces utilized in the later processing of the strip.

When the strip 66 has' reached a suiilcient length, theremovable lsection of the roller table ismoved so as to permit the strip to hang freely within the furnace, as shown in Fig. 7. It will be noted that theonly portion of the furnacev which is open to thev atmosphere is the relatively narrow opening at the top, and this passage is sealed from the atmosphere'by means of flame sheets 14 provided by the burners 13, whereby the entire process is carried out under the eifect of a I -have provided mechanically driven rollers 15, whereby upon completion ofthe rolling process, the strip 66 may be lifted out of the p it furnace so that it may be cut by means of the shears 12 and coiled upon the coller 1I located conveniently adjacent the mill 69. After coiling, the strip which is at a relatively high temperature of approximately 700 to 800 C. is fed into a cooling apparatus.' y

Referring now to Figs. 8, 9, and 10 which show two modifications of a cooling apparatus in which the strip is cooled in a special atmosphere and if desired under partial vacuum prior to a subsequent cold rolling operation. In Fig. 8 a base 9| is provided with grooves for providing a liquid y ports the lining 86 and the exible angle 89 provides in conjunction with-the liquid 90 the necessary seal during the removal of the gas from the lid 80 through the pipe 85. Gas inlet and outlet pipes are shown respectively at 83 and 84, and hese may also be used to flush the chamber with lsuitable gas. In Fig. 10 I have shown an alternate arrangement in whicha fluid seal is provided which will permit of partial evacuation of the annealing chamber. For this purpose, of course, the sealing liquid must extend considerably higher than in the other case. But generally speaking, the principles of the devices 0f Figs. 8 and 1I) are the same. I

- Other arrangements may also .be used for cooling the strips. In some instances, particularly in cases where the finished temperature of the rolling process is too low, it is advantageous furnace with a corresponding cooling chamber, so that the strip is re-heated and then cooled. With this latter arrangement a better access of the special atmosphere into the strip surface is accomplished.

The hereinabove described refining process and modification of the contents of various constituents, as for example,-carbon, sulphur gases, etc., with the diffusion method may be advantageously applied to other processing methods. .For example, a bi-metallic ingot can be produced by pouring small amounts of dissimilar metal into the r tating mold. Alternatively the inner surface of the mold may be covered with the dissimilar metal, such as chromium, copper, nickel, aluminum and other metals, either individually or in alloyed form. Or the inner surface of such mold may be lined with a paste containing such metal or metals either free or chemically bound. It may also be heat-insulated, to make the adsorption of such alloy metals more complete. These metals fully dissolved by the liquid parent metal or partially dissolved by the solidied parent metal, will form an alloy skin on the surface of the hollow ingot. The above described further processing in the pit furnace produces a further advantageous diffusion under reducing conditions, as well as the addition of gases which advantageously effect the quality and properties of the skin, with respect to, for example, corrosion resistance. -Subsequent processing of the coils in the annealing and cooling furnaces leads to a partial absorption of the alloy metal on the other side of the strip, whereby an alloy skin is provided on both sides thereof.

Modifications may be made in my invention without departing from the spirit thereof, and I do. not intend to limit myself otherwise than as pointed out in the claims which follow.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A process for the production of rened steel strip of fine gauges from a less refined molten metal, which includes the steps of producing an ingot of relatively thin section and preferably hollow shaped, and subjecting said ingot to an initial heat treating operation under the influence of a reducing atmosphere in a furnace, then to a rolling operation in a mill, and thereafter alternating heat treating operations with rolling operations to obtain a further refinement of the metal by a combined atmosphere and temperature action upon the said metal, improving chief- 'ly the condition of the surface layer of metal while on account ofv said rolling operations, said surface layer increases in relation to the weight.

2. A process of producing refined steel stock of iine gauges in accordance wtih claim 1, which includes the step of reducing the stock in the form of an endless belt 'and passing said belt through a chamber containing reducing gases.

3. 'A process for producing rolled metal stock `which comprises centrifugally casting molten metal to form a hollow ingot, heat treatingsaid hollow ingot, inserting said ingot over a roll of a rollng mill,v rolling said ingot in said mill, and during said rolling causing the metal being rolled to pass over an additional stationary roll and an additional movable roll, and applying force to said movable roll` to exert Va tension on said metal while being rolled. l

4. A process for producing rolled metal stock which comprises centrifugally casting molten metal to form a hollow ingot, heat treating said hollow ingot, inserting said ingot over a roll of a rolling mill, rolling said ingot in said mill, and during said rolling causing the metal being rolled to pass over an additiona stationary roll and an additional movable roll, and applying force to said movable roll to exert a tension on said metal while being rolled, cutting and colling the metal after rolling, and further refining said metal by heat treating it in the presence of a reducing gas.

5,. A process for producing rolled metal stock which comprises centrifugally casting molten metal to form a hollow ingot, heat treating said hollow ingot, inserting said ingot over a roll of l a rolling mill, rolling said ingot in said mill, and

during said rolling causing the metal being rolled to pass over an additional stationary roll and an additional movable roll, and applying force to said movable roll to exert a tension on said metal while being rolled, maintaining a portion of the metal during rolling under heat in a reducing atmosphere, and finallyl cutting and colling the metal after rolling, and further rening said metal by heat treating it in the presence of a reducing gas.

6. A process for the productionof refined steel strip of fine gauges from less rened metal which includes the steps of producing an ingot of a relatively thin section and rolling it in successive steps to the desired gauge, forming at least before thefirst rolling step a refined surface layer on the processed stock by heating it in thepresence of a reducing gas for suillcient length to form a layer which completely encloses said stock, and through its improved rolling qualities protects the cohesion of the less refined metal during said rolling operations.

'7 A process of producing strip by rolling from cast metal relatively high in impurities and normally unsuitable'for rolling, which. comprises casting al thin-walled ingot from said metal, then heat-treating said ingot under a reducing atmos- 'phere for a sufficient length of time and at a suf- 8. A process of producing strip by rolling from A cast metal relatively high in impurities an'd normally unsuitable for rolling, which comprises casting a thin-walled ingot from said metal, then heat-treating said ingot under a reducing atmosphere for a sufficient length of time and at a sufficient temperature to refine a surface layer of said metal ingot, then transferring said ingot to a mill and hotrolling it in a plurality of passes, and intermediate said passes protecting surface layers of said metal by heat treating it in a reducing atmosphere.

9. A process of producing strip by rolling from cast metal relatively high in impurities and normally unsuitable for rolling, which comprises casting a thin-walled ingot from said metal, then heat-treating said ingot under a reducing atmosphere for a sufcient length of time and at a,

sufficient temperature to refine a surface of said metal ingot, then transferring said ingot to a mill and hot rolling it, said heat treatment being concluded with a treatment under a reduced pressure whereby to remove from' said surface layer of the metal absorbed gases.

10. A process of producing strip by rolling from cast metal relatively high in impurities and normally unsuitable for rolling, which comprises casting a thin-walled ingot from said metal, then heat-'treating said ingot under a reducing atmosphere for a sufficient length of time and 'at a sucient temperature to renne a surface layer of said metal ingot, then transferring said ingot to a mill and hot rolling it in a plurality of passes, and intermediate said passes protecting surface layers of said metal by heat treating it in a reducing atmosphere, nally heat treating the hot-reduced strip in a reducing atmosphere toy further rei-lne it, and further reducing the strip by cold rolling,

11. A process of producing strip metal from a metal normally unsuitable for rolling and relatively high in impurities, which comprises casting said metal to form a hollow ingot, then heat treating said ingot in a furnace under a reducing atmosphere at sufcient temperature and for a suicient length of time to rene a-surface layer of said metal so that the ingotv may. be hot rolled, then transferring said ingot to a mill, placing it over a roll thereof, and hot rolling said ingot to strip form.

12. A process of producing strip metal from a metal normally unsuitable for rolling and relatively high in impurities, which comprises casting said metal to form a hollow ingot, then heat treating said ingot in a furnace under a reducing atmosphere at sufficient temperature and fora sufdcient length of time to refine a surface layer of said metal so that the ingot may be hot rolled, then transferring said ingot to a mill, placing it over a roll thereof, and hot rolling said ingot to strip form and while so hot rolling said ingot causing a portion thereof to lie within a heated furnace having a reducing atmosphere.

13. A process ,of producing strip metal from a metal normally unsuitable for rolling and rela-y tively high in impurities, which comprises casting said metal to form a hollow ingot, then heat treating, said ingot in a furnace under ahreducing atmosphere at suilicient temperatureand for a sufiicient length of time to renne a surface layer of said metal so that the ingot may be hot rolled, then transferring said ingot to a mill, placing it over a roll thereof, and hot rolling said ingot .to strip form and while so hot rolling said ingot causing a portion thereof to lie within a heated furnace having a reducing atmosphere, nally shearing and coiling the strip material so formed, heat treating it in areducing atmosphere so as to increase the ratio of the thickness of the rened skin to the total thickness, and cold rolling the thus treated strip, then again annealing it in a reducing atmosphere to further increase the said ratio.

14. Process for rening steel according to claim 1 including a heat treatment ofthe steel ingot in a heat treating chamber adapted to withstand high temperatures and with a gas-tight seal and connections for the supply and evacuation of gases and consisting in bringing it in contact for a while with suitable gases preferably circulating while at an elevated temperature and immediately 4afterwards evacuating the greatest portion of said gases thereby creating a partial vacuum in said heat treating chamber and so causing most of the gases used for the treatment and which became absorbed in said steel ingot, to 4 escape.

15. Process for refining steel according to claim 1 including the step of hot-reducing the steel ingot in the form of an endless belt and passing said belt through a chamber containing nonoxidizing gases, which step consists of supplying said object to the mill from a chamber lled with non=oxidizing gases and withdrawing it from said mill into a similar chamber While protecting it from oxidation on its way to and from the mill and while in said mill by ame walls,

16. Process for rening steel according to claim 1 including the step of rolling the ingot in the form of an endless belt and passing said belt 4through a chamber containing non-oxidizing gases, in which process the step of hot rolling is first carried out without protective atmosphere as long as the steel object is relatively thickand stiff, and afterward a part of the metal is allowed to run through said chamber having a non-oxidizing atmosphere.

TADEUSZ SENDZIMIR. 

